Tilemap has gap between tiles, how do I get rid if it.

I've created a script that creates a bunch of tiles, but all of the tiles have a gap between them, what is a good way to get rid of the gaps.

Here's a picture:

here's the code used to generate the tiles

 using UnityEngine;
 using System.Collections;
 
 public class TileLoader : MonoBehaviour{
     public GameObject prefabTile;
     public int TileWidth = 16;
     public int TileHeight = 16;
     public int size = 3;
     
 
     // Use this for initialization
     void Start () {
     loadTile();
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
     
     void loadTile()
     {
         for(int i=0; i < TileWidth; i++)
             for(int j=0; j<TileHeight;j++)
         {
             GameObject tile = Instantiate(prefabTile, new Vector3(i*size,0,j*size),Quaternion.Euler(0,0,0)) as GameObject;
             tile.transform.parent = transform;
         }    
     }
     
 }